the patch is missing the documentation of the hFill & vFill properties in the GridCtorArgs object.

the patch introduces a module name define(name, []). It should not.

some very minor optims from the old code are not here anymore (like not calling getTransformerFromModel several times for the same axis/scaler)

SimpleTheme.js "grid" part must be modified to support the new fill style properties.

I think we should not draw either lines or rectangles in two totally distinct code paths as you do. We should draw lines if v/hMajor/MinorLines is true as we do today. And rectangles _without_ stroke if v/hFill is here. Otherwise this is confusing as this creates two modes that ignore each others with two ways of setting line colors (regular way + the stroke of the rectangles).

Shouldn't all of this work only on major ticks? That would avoid the ticks sorting... And it seems to me that putting fills between each minors tick would bloat the screen? I'm not sure about that one. I wonder if you have the use-case of filling between minor ticks?

Some enhancement suggestions:

shouldn't we support filling with more than colors? If we just support color maybe better calling the property color than fill.

shouldn't we provide fill & alternateFill instead of forcing no filling on each other interval? That would be more flexible.